Recently it has become apparent that the egg plasma membrane is modified during fertilization and that these changes may play a role in the activation of egg metabolism and development. The objective of this project is to characterize the integral and peripheral proteins of the sea urchin egg plasma membrane, determine how they are modified at fertilization and evaluate the role of cortical vesicle exocytosis in bringing about these changes. The project will involve the following: 1) Further characterization of the egg plasma membrane proteins by selective extraction procedures and radiolabelling techniques. 2) Isolation of the cortical secretory vesicles and characterization of the soluble and membrane bound components. 3) Isolation of the plasma membrane from fertilized eggs and evaluation of the changes in polypeptide organization and content which occur at fertilization and 4) Determination of the role that the cortical vesicles play in these changes, including incorporation of vesicle components into the plasma membrane and enzymatic modification of cell surface proteins. In addition to basic information on the egg plasma membrane and its interaction with the cortical secretory vesicles, this work will serve as a basis for future investigations of the role of these cell surface changes in regulating metabolism and development.